In the early years of commercial air transport, the National Airspace System, used by commercial airlines, comprised of controlled and uncontrolled airspace. Aircrews would typically begin a flight on an instrument flight regulations (IFR) route directed by Air Traffic Control. At a downstream waypoint in the flight, aircrews would enter uncontrolled airspace or visual flight regulations (VFR) airspace which was not supervised by Air Traffic Control. In uncontrolled airspace, aircrews were responsible for visually identifying and avoiding other aircraft. In 1956, two commercial airlines collided over the Grand Canyon while operating in uncontrolled VFR airspace. All crew and passengers perished in the collision. As a result of this tragedy, sweeping changes to the National Airspace System were developed and implemented for safer commercial flight operations. Today, the National Airspace System at an altitude above 10,000 feet (higher or lower depending on the geographic location) is all controlled airspace managed by Air Traffic Control of the Federal Aviation Administration. No aerospace vehicle may operate in FAA controlled airspace without first meeting stringent requirements for vehicle flight airworthiness, on-board communications and avionics equipment, air traffic patterns and routes, and many other safety related aspects. In uncontrolled airspace at altitudes below 10,000 feet, aviation operations include model/experimental aircraft, general aviation aircraft, helicopters, gliders, and skydiving operations. These activities are subject to separate but less stringent FAA regulations.
As a general overview, FIG. 1 is a representation of the current National Airspace System (NAS). Generally, the NAS includes classes of airspace: Class A, B, C, D, E, and G. Each class is governed by laws and regulations regarding operation of aircraft type, aircraft equipment required, and how an aircraft may operate with the class. Class A airspace extends from 18,000 feet MSL to FL 600 (or 60,000 feet MSL). Unless otherwise authorized, all aircraft must be operated under Instrument Flight Regulations (IFR). Class B airspace extends from the surface to 10,000 feet MSL surrounding the nation's busiest airports. Class C airspace extends from the surface to 4,000 feet above the airport elevation surrounding those airports that have an operation control tower, are serviced by a radar approach control, and that have a certain number of IFR operations. Class D airspace extends from the surface to 2,500 feet above the airport elevation surrounding those airports that have an operation control tower. Class E airspace is controlled airspace that is not Class A, B, C, or D. Class G airspace is uncontrolled airspace that is not designated as Class A, B, C, D, or E. FIG. 1 illustrates more Class E airspace than Class G airspace. However, generally, Class G airspace (uncontrolled) is most abundant, away from large cities.
While the first 100 years of aviation history have been focused on manned aircraft operating in the National Airspace System, there has recently been a surge of interest in unmanned aerial systems (UASs). For example, in the past 10+ years, the Department of Defense has placed great emphasis on acquisitioning and employing UASs in support of combat operations. In the Iraq War (Operation Iraqi Freedom) and the War in Afghanistan (Operation Enduring Freedom), several types of high-altitude and low-altitude UASs have been utilized. However, interest in UASs is not limited to military operations. A number of civilian UASs have been designed for commercial purposes. The rapidly increasing interest and employment of civilian UASs for commercial gain raises many safety concerns, given the current, limited regulations at lower altitudes. Our current National Airspace System generally is limited to controlling airspace above 10,000 feet (higher or lower in some areas). A civilian UAS operating over 10,000 feet would need to comply with all FAA rules and regulations regarding aircraft airworthiness, equipment requirements, following ATC instructions and routes, etc. However, civilian UASs operating at low-altitude, below 10,000 feet, are not subject to such regulations. As such, low-altitude UASs operations are very limited. Yet, the potential benefit of low-altitude UASs operations is becoming increasingly apparent. For example, low-altitude UASs may be utilized for delivery of goods and services in urban and rural areas, imaging and surveillance for agricultural, infrastructure and utility management, and medical product/service delivery.
The Federal Aviation Administration (FAA) is working on a system to enhance safety and efficiency in the National Airspace System above 10,000 feet MSL by employing the Automatic Dependent Surveillance-Broadcast (ADS-B) system. FIG. 2 illustrates where ADS-B will be implemented in the NAS, while FIG. 3 shows an implementation model of ADS-B. ADS-B is an environmentally friendly technology that enhances safety and efficiency, and directly benefits pilots, controllers, airports, airlines, and the public. It forms the foundation for Next Generation Air Transportation System or NextGen by moving from ground radar and navigational aids to precise tracking using satellite signals. With ADS-B, pilots for the first time see what controllers see: displays showing other aircraft in the sky. Cockpit displays also pinpoint hazardous weather and terrain, and give pilots important flight information, such as temporary flight restrictions.
ADS-B reduces the risk of runway incursions with cockpit and controller displays that show the location of aircraft and equipped ground vehicles on airport surfaces—even at night or during heavy rainfall. ADS-B applications being developed now will give pilots indications or alerts of potential collisions. ADS-B also provides greater coverage since ground stations are so much easier to place than radar. Remote areas without radar coverage, like the Gulf of Mexico and parts of Alaska, now have surveillance with ADS-B.
Relying on satellites instead of ground navigational aids also means aircraft will be able to fly more directly from Point A to B, saving time and money, and reducing fuel burn and emissions. The improved accuracy, integrity and reliability of satellite signals over radar means controllers eventually will be able to safely reduce the minimum separation distance between aircraft and increase capacity in the nation's skies.
Only ADS-B Out is mandated, and only within certain airspace. Title 14 CFR § 91.225 defines the airspace within which these requirements apply. On Jan. 1, 2020, when operating in the airspace designated in 14 CFR § 91.225 one must be equipped with ADS-B Out avionics that meet the performance requirements of 14 CFR § 91.227. Aircraft not complying with the requirements may be denied access to this airspace. Under the rule, ADS-B Out performance will be required to operate in: 1) Class A, B, and C airspace; 2) Class E airspace within the 48 contiguous states and the District of Columbia at and above 10,000 feet MSL, excluding the airspace at and below 2,500 feet above the surface; 3) Class E airspace at and above 3,000 feet MSL over the Gulf of Mexico from the coastline of the United States out to 12 nautical miles; and 4) Around those airports identified in 14 CFR part 91, Appendix D.
ADS-B Out is the ability to transmit a properly formatted ADS-B message from the aircraft to ground stations and to ADS-B-In-equipped aircraft. ADS-B In is the ability of an aircraft to receive information transmitted from ADS-B ground stations and from other aircraft. ADS-B In is not mandated by the ADS-B Out rule. If an operator chooses to voluntarily equip an aircraft with ADS-B In avionics, a compatible display is also necessary to see the information.
While the FAA's ADS-B system appears promising for enhancing air traffic capabilities for large aircraft (for example, commercial airliners) above 10,000 feet MSL, it may not be feasible to implement the system with small UASs and general aviation aircraft operating under 10,000 feet MSL.
Referring now to FIG. 4, another traffic management system being implemented in the U.S. is the Automatic Identification System (AIS) for automatically tracking ships and other nautical vessels. Managed by the U.S. Coast Guard, AIS is a maritime navigation safety communications system standardized by the International Telecommunication Union (ITU) and adopted by the International Maritime Organization (IMO) that provides vessel information, including the vessel's identity, type, position, course, speed, navigational status and other safety-related information automatically to appropriately equipped shore stations, other ships, and aircraft; receives automatically such information from similarly fitted ships; monitors and tracks ships; and exchanges data with shore-based facilities.
The AIS is a shipboard broadcast system that acts like a transponder, operating in the VHF maritime band, that is capable of handling well over 4,500 reports per minute and updates as often as every two seconds. It uses Self-Organizing Time Division Multiple Access (SOTDMA) technology to meet this high broadcast rate and ensure reliable ship-to-ship operation. Each AIS system consists of one VHF transmitter, two VHF TDMA receivers, one VHF DSC receiver, and standard marine electronic communications links (IEC 61162/NMEA 0183) to shipboard display and sensor systems. Position and timing information is normally derived from an integral or external global navigation satellite system (e.g. GPS) receiver, including a medium frequency differential GNSS receiver for precise position in coastal and inland waters. Other information broadcast by the AIS, if available, is electronically obtained from shipboard equipment through standard marine data connections. Heading information and course and speed over ground would normally be provided by all AIS-equipped ships. Other information, such as rate of turn, angle of heel, pitch and roll, and destination and ETA could also be provided.
AIS normally works in an autonomous and continuous mode, regardless of whether it is operating in the open seas or coastal or inland areas. Transmissions use 9.6 kb GMSK FM modulation over 25 or 12.5 kHz channels using HDLC packet protocols. Although only one radio channel is necessary, each station transmits and receives over two radio channels to avoid interference problems, and to allow channels to be shifted without communications loss from other ships. The system provides for automatic contention resolution between itself and other stations, and communications integrity is maintained even in overload situations.
Each station determines its own transmission schedule (slot), based upon data link traffic history and knowledge of future actions by other stations. A position report from one AIS station fits into one of 2250 time slots established every 60 seconds. AIS stations continuously synchronize themselves to each other, to avoid overlap of slot transmissions. Slot selection by an AIS station is randomized within a defined interval, and tagged with a random timeout of between 0 and 8 frames. When a station changes its slot assignment, it pre-announces both the new location and the timeout for that location. In this way new stations, including those stations which suddenly come within radio range close to other vessels, will always be received by those vessels. The required ship reporting capacity according to the IMO performance standard amounts to a minimum of 2000 time slots per minute, though the system provides 4500 time slots per minute. The SOTDMA broadcast mode allows the system to be overloaded by 400 to 500 percent through sharing of slots, and still provide nearly 100 percent throughput for ships closer than 8 to 10 NM to each other in a ship to ship mode. In the event of system overload, only targets further away will be subject to drop-out, in order to give preference to nearer targets that are a primary concern to ship operators. In practice, the capacity of the system is nearly unlimited, allowing for a great number of ships to be accommodated at the same time.
The system coverage range is similar to other VHF applications, essentially depending on the height of the antenna. Its propagation is slightly better than that of radar, due to the longer wavelength, so it's possible to “see” around bends and behind islands if the land masses are not too high. A typical value to be expected at sea is nominally 20 nautical miles. With the help of repeater stations, the coverage for both ship and VTS stations can be improved considerably.
The U.S. Coast Guard has developed rules applicable to both U.S. and foreign-flag vessels that require owners and operators of most commercial vessels to install and use the AIS. The AIS rule is part of a domestic and international effort to increase the security and safety of maritime transportation. Current AIS regulations, 33 CFR § 164.46, became effective on Nov. 21, 2003, and, require that all vessels denoted 33 CFR § 164.46(a) be outfitted with an USCG ‘type-approved’ and ‘properly installed’ AIS no later than Dec. 31, 2004.
Shipboard AIS units autonomously broadcast two different AIS messages: a ‘position report’ which includes the vessels dynamic data (e.g. latitude, longitude, position accuracy, time, course, speed, navigation status); and, a ‘static and voyage related report’ which includes data particular to the vessel (e.g. name, dimensions, type) and regarding its voyage (e.g. static draft, destination, and ETA). Position reports are broadcasted very frequently (between 2-10 seconds—depending on the vessels speed—or every 3 minutes if at anchor), while static and voyage related reports are sent every six minutes; thus it is common and likely that an AIS user will receive numerous position reports from a vessel prior to receipt of the vessels' name and type, etc.
AIS users are required to operate their unit with a valid MMSI, unfortunately, some users neglect to do so (for example, use: 111111111, 123456789, 00000001, their U.S. documentation number, etc.). A valid MMSI will start with a digit from 2 to 7, a U.S. assigned MMSI will start with either 338, 366, 367, 368, or 369. AIS users whom encounter a vessel using MMSI: 1193046 or named: NAUT should notify the user that their AIS unit is broadcasting improper data. All AIS users should check the accuracy of their AIS data prior to each voyage, and, particularly units that have been shutdown for any period of time.
While the U.S. Coast Guard's Automatic Identification System appears promising for enhancing traffic capabilities for nautical vessels, it is not directly transferable to aviation applications, as AIS is two-dimensional (i.e., tracks vessels on the surface of the earth), and AIS requires a human (a navigator of a vessel) to view a display and make course corrections based on AIS information and other marine navigation equipment.
Several efforts to integrate civilian UASs into the National Airspace System have been proposed. However, none of these have addressed civilian low-altitude applications, and thus economic development is being stifled. Some people have recognized this dilemma and have proposed various ways to increase UASs flight safety. For example, U.S. Pat. No. 7,269,513 to Herwitz (funded by NASA under a Cooperative Agreement) describes a ground-based sense-and-avoid display system (SAVDS) for unmanned aerial vehicles. SAVDS integrates airborne target position data from ground-based radar with unmanned aerial vehicle (UAV) position data from the UAV ground control station (GCS). The UAV GCS receives the UAV position data from a global positioning system (GPS) element in the flight management autopilot system in the UAV. Using a high-resolution display, the SAVDS shows the GPS position of the UAV in relation to other radar-detected airborne targets operating in the same airspace. With the SAVDS co-located adjacent to the GCS computer controlling the UAV, the SAVDS instructs the UAV operator to change the heading and/or elevation of the UAV until any potential midair aircraft conflict is abated. The radar-detected airborne target data and the UAV GPS data are integrated and displayed with geo-referenced background base maps that provide a visual method for tracking the UAV and for performing collision avoidance. (Abstract).
Another UASs safety-related invention is U.S. Pat. No. 8,358,677 to Collette et al. This patent describes a system and method for transmitting UAV position data to a central flight control center transmits UAV position data using a virtual transponder. A ground control station for controlling the UAV receives data from the UAV, including UAV position data. The UAV may provide GPS data, or corrected position data based on readings from an inertial navigation system. The ground control station transmits the UAV position data to a flight control center. (Abstract).
Furthermore, U.S. Pat. No. 8,386,175 to Limbaugh et al. (funded by the U.S. Air Force under contract) describes a UAS position reporting system. Implementations may include an air traffic control reporting system (ATC-RS) coupled with a ground control station (GCS) of an unmanned aerial system where the ATC-RS includes an automatic dependent surveillance broadcast (ADS-B) and a traffic information services broadcast (TIS-B) transceiver and one or more telecommunications modems. The ATC-RS may be adapted to receive position data of the UAS in an airspace from the GCS and communicate the position of the UAS in the airspace to a civilian air traffic control center (ATC) or to a military command and control (C2) communication center through an ADS-B signal or through a TIS-B signal through the ADS-B and TIS-B transceiver. The ATC-RS may also be adapted to display the position of the UAS in the airspace on one or more display screens coupled with the ATC-RS. (Abstract).
Finally, U.S. Patent Application Publication No. 2008/0033604 to Margolin describes a system and method for safely flying an unmanned aerial vehicle (UAV), unmanned combat aerial vehicle (UCAV), or remotely piloted vehicle (RPV) in civilian airspace that uses a remotely located pilot to control the aircraft using a synthetic vision system during at least selected phases of the flight such as during take-offs and landings. (Abstract).
These and other inventions seek to improve flight operations safety for UASs. However, past ideas for using UASs commercially have only focused on individual safety aspects of UASs operations, not the entire system. For example, for our road transportation system, there are traffic regulations, traffic signs, and traffic signals. For Visual Flight Rules (VFR) and Instrument Flight Rules (IFR) flight operation systems, there are rules, regulations, flight procedures, and an FAA air traffic management system providing control and support. However, none of the rules and regulations of our current ground transportation safety systems or current national airspace safety systems apply to the traffic management of UASs operating at low-altitude. There is a gap in our nation's transportation safety regulation systems and a lack of infrastructure to support low-altitude UASs operations. Moreover, there have been restrictions on use of UASs operations inside the National Airspace System, particularly in Class A, B, C, and D airspace.
What is needed, and what the present invention provides, is an overall UASs traffic management system (UTM) for low-altitude UASs operations, for example, in Class G airspace. UTM fills the gap between our nation's ground transportation system and National Airspace System. While the NAS is rigidly controlled by the FAA, UTM is more automated and requires very little or no Air Traffic Control oversight. It is recognized, however, that there could be some overlap or touch points where NAS operations may use similar altitudes during transition phases of flights for UASs. For these touch points, UTM accounts for airspace design, automation for scheduling and de-confliction, or a combination of the two, to seamlessly integrate UTM airspace and NAS airspace.
The characteristics of UTM, including the integration of hardware, software, automation, and flight procedures, are essential for preventing mid-air collisions in uncontrolled airspace, like the devastating accident over the Grand Canyon in 1956, and equally important, preventing mid-air collisions for UASs over highly populated areas. Furthermore, the next 100+ years of aviation history will likely be dominated by unmanned vehicles, and possibly personal, manned aircraft. Using the lessons learned from today's Air Traffic Management system, UTM is essential to enable the accelerated growth of commercial and personal UASs applications. UTM enables civilian applications of micro, small, and medium size UASs to generate more economic value from airspace operations particularly at lower altitude and largely underutilized airspace, for example Class G airspace, and other non-FAA controlled airspace.